The present invention relates to automotive vehicle brake lathes configured for resurfacing brake rotor components, and in particular to vehicle brake lathes utilizing variable speed drive motors.
One of the main components of a vehicle wheel braking system employing disk brakes are the brake disks, or brake rotors, which provide a solid rotating surface against which the stationary brake friction pads are clamped or compressed to generate a frictional force, slowing the rotational movement of the brake disks or brake rotors and the associated vehicle wheels. The brake disks or brake rotors are subjected to repeated and substantial frictional forces by the brake friction pads, and over time, become worn. Uneven application of braking force, debris, or uneven frictional surfaces on the brake friction pads can result in the formation of grooves, channels, or scratches in the surfaces of the brake disks or brake rotors. Repeated heating and cooling of the brake disk or brake rotor resulting in extreme temperature variations can additionally result in the lateral warping of the brake disk or brake rotor.
A worn or warped brake disk or brake rotor may be resurfaced by cutting or grinding to provide a uniform smooth brake friction pad contact surface if sufficient brake disk or brake rotor material remains to provide an adequate braking surface without compromising the structural integrity of the vehicle braking system. However, once a brake disk or brake rotor has been worn below a minimum safe thickness, it is unable to safely dissipate the heat generated by a brake application, and must be replaced.
To provide for a uniform surface, any abnormalities in the brake disk or brake rotor, such as a lateral warping must be detected and removed during the resurfacing procedures. An additional source of lateral warping defects in a brake rotor or brake disk is often over tightened attachment bolts or an uneven mounting surface onto which the brake disk or brake rotor is secured in the vehicle wheel assembly. If the brake disk or brake rotor is removed from the vehicle wheel assembly for a resurfacing operation on a fixed or “bench” brake lathe any abnormalities or defects resulting from the mounting of the brake disk or brake rotor to the vehicle wheel assembly may not be accurately identified or corrected during the resurfacing procedure. Accordingly, a variety of brake resurfacing machines or brake lathes have been developed to resurface brake disks and brake rotors while they remain mounted to the vehicle wheel assembly.
Brake resurfacing machines or brake lathes configured to resurface brake disks and brake rotors mounted to a vehicle wheel assembly are commonly referred to as on-car brake lathes. One example of an on-car brake lathe is the OCL-360 brake lathe sold by Hunter Engineering Co. of Bridgeton, Mo. By eliminating the need to remove the brake disk or brake rotor from the vehicle wheel assembly, the overall efficiency of the resurfacing procedure is improved, and the chances for operator induced error are reduced.
Traditionally, on-car and bench brake lathes, such as the BL501/BL505 off-car brake lathe sold by Hunter Engineering Co. of Bridgeton, Mo., utilize motors or drive systems configured for operation at a fixed spindle RPM and feed rate. During rotor cutting or resurfacing, a resonance or vibration, commonly referred to as “chatter”, can develop between the rotor cutting tools and the rotor surface, resulting at best in an uneven resurfacing of the brake rotor, or at worst, in severe damage to the rotor surface or rotor cutting tools themselves. Accordingly, the fixed spindle RPM and feed rates in traditional on-car and bench brake lathes are selected to be below the rates at which the resonance or vibration is likely to occur. However, since the rates at which the resonance or vibration are likely to occur vary for different types of brake rotors, there is a need for on-car and bench brake lathes having improved drive motor systems, which are capable of varying the spindle RPM during the resurfacing of a rotor and, optionally, the feed rate, up to a maximum rate at which a desired brake rotor resurfacing quality can be achieved, thereby reducing operator time require to resurface a brake rotor and providing enhanced safety features, such as automatic motor speed reduction or shutoff during abnormal operating conditions.
Some vehicles are equipped with locking differentials in the vehicle drive train that engage when a difference in wheel rotational speed from one side of the vehicle to the other reaches approximately 100 RPM. When the locking mechanism engages, as may occur during rotation of a brake rotor by an on-car brake lathe, the resulting change in rotational resistance can violently rotate the entire on-car lathe body. It is desirable to provide an on-car brake lathe with safety features configured to automatically stop the lathe rotation if a sudden resistance is encountered in the cut.